The predictive utility of using psychological variables to explain performance differences not accounted for by differences in physiological capacity was explored. It was hypothesized that psychological variables would affect performance directly as well as by modifying the relationship between physical capacity and performance. VO2 max, attraction to physical activity, estimation of physical ability, and the psychological defenses of reversal and turning against self were employed to predict performance by Navy recruits in a 3.62 km (2.25-mile) run. A stepwise multiple regression procedure entered V02 max as the first predictor of performance followed by the psychological variables and then the interactions between V02 max and the psychological variables. The evidence indicates that psychological variables should be included in models of performance for physical tasks. Such models will probably incorporate situation-specific psychological variables (e.g., elements of situational motivation) to fully understand and psychological dynamics connecting general personality measures and performance.